【発明の詳細な説明】[Detailed description of the invention]
本発明は、磁性トナーを用いる現像装置に関す
る。
従来電子写真、静電記録等における現像方法と
しては、大別して乾式現像法と湿式現像法とがあ
る。前者は更に、二成分系現像剤を用いる方法
と、一成分系現像剤を用いる方法とに二分され
る。一成分系現像方法は、二成分系現像方法にお
けるトナーとキヤリヤの混合比の変化による顕画
像の濃度の変動、キヤリヤの長時間使用による劣
化に原因する画質の低下等の欠点がない点に於て
優れている。
一成分系現像方法に属するものの中、所謂ジヤ
ンピング現像法を除く他のパウダクラウド法、ト
ナー粒子を直接静電潜像面に接触させるコンタク
ト現像又はドナー現像といわれる方法、磁性の導
電性トナーを静電潜像面に接触させるマグネドラ
イ法は、何れも被現像面の全面即ち画像部・非画
像部共にトナーが接触するため、非画像部にまで
トナーが付着し所謂地カプリとなつて汚れが生じ
易い問題がある。
ジヤンピング現像法は、シート等の支持体にト
ナーを均一に塗布した後、これを静電像保持面に
小間隔を保つて対向させ、静電潜像の有する電荷
により、トナーを支持体から吸引して潜像保持面
に付着させて現像する方法である（特公昭41−
9475号公報・米国特許第2839400号明細書等）。
この方法は、静電荷のない非画像部では、トナ
ーが吸引されないばかりか、トナーと、非画像面
とが接触しないので、上記他の一成分系現像法の
カプリが出にくいという長所がある。しかしなが
ら現像剤支持手段にトナーの実用的な均一塗布が
困難である。繰り返し使用に対し現像剤を凝集さ
せることなく、現像剤支持手段上に塗布し維持さ
せることが困難であるため、その実用化には問題
がある。
そこで本出願人は、特開昭54−43037号公報に
開示したように、磁性体又は磁石から成る厚み規
制手段（以下磁性ブレードという）により、現像
剤支持体上にトナー厚を規制しながら塗布する方
法を開発した。
また、ジヤンピング現像法は、γ特性が高く階
調再現性が悪い傾向があるので、この点に関して
も特開昭55−18656号発明の、現像剤支持手段と
静電潜像保持手段との間に低周波交流電圧を現像
バイアス電界として印加することにより改善し
た。
本発明は、磁性体を有する現像剤層を担持して
回転し、潜像保持体との最近接間隙を形成する現
像部位に搬送する現像剤担持体と、上記現像部位
に交互電界を印加する手段と、上記現像剤担持体
の内側に配置された固定磁石であつて、上記現像
部位が２つの異なる極性の磁極間に位置するよう
に配置された固定磁石と、を備えた現像装置であ
る。
即ち、本発明では現像部位に交互電界が印加さ
れる。この交互電界により現像剤は現像剤担持体
から潜像保持体に転移せしめられ、次に潜像保持
体から離脱せしめられるという工程を繰り返し、
最終的に潜像電位に応じた現像剤量の付着を得て
現像がなされるものである。
而して本発明では、上記交互電界が印加される
現像部位は、現像剤担持体に内包さた固定磁石の
２つの異なる極性の磁極間に位置している。従つ
て、現像部位には上記２つの磁極間に形成される
磁気閉回路が作用する。この磁気閉回路は磁力線
に沿つて鎖状に連なつた現像剤を現像剤担持体側
に寝かせて現像剤担持体側への現像剤拘束力を強
くする。これにより、前記交互電界の前記転移方
向の位相時に現像剤を現像剤担持体から潜像保持
体の非画像部にそれを越えて転移せしめる閾値が
大きくなり、非画像部への現像剤転移を抑制し、
その結果現像剤を交互電界により潜像保持体に繰
り返し転移させる方式の現像装置であるにもかか
わらず、カブリ防止効果を向上させる効果を持つ
ものである。
なお本発明は、潜像保持体の構成、潜像形成プ
ロセス等には関係なく、カールソンプロセス、本
出願人のNPプロセスその他磁気的記録装置に適
用される。
以下図面について詳述する。第１図に於て１は
内包する固定磁石２の周囲に回転する現像剤担持
体としてのスリーブ、３はスリーブ１と対向する
磁性体（例えば鉄製）のトナー層厚規制部材（ブ
レード）であつて、対向する磁極N1とで形成す
る磁界により、トナー４のスリーブ１上への塗布
の厚みを規制する。潜像保持体５は例えば正の電
位パターンを有する感光ドラムであつて、スリー
ブ２と同方向に略同速で回転する。スリーブ１と
ドラム５は、その最近接部の近傍で現像領域Ｄを
形成する。その領域Ｄでの両者１，５の間隙Ａ
は、スリーブ１・ブレード３間の間隙Ｂより大き
く形成する。
６はスリーブ１・ドラム５間に印加する交流電
圧バイアス電源であつて、接地された感光ドラム
５の背面電極とスリーブ１の軸とに接続した例を
示す。その交流電圧は例えば第２図に示す歪正弦
波交流とする。この交互（交番）電界により現像
領域Ｄに於てトナーを往復運動させて現像を促進
する。
第１図は磁極S1を感光ドラム５とスリーブ１の
最近接部の近傍に位置させた従来提案されている
例である。
この例に於て次の仕様を有している。
間隙（μ）
Ａ＝300 Ｂ＝250
磁極のスリーブ上の磁力密度（ガウスＧ）
S1＝650
N1＝850
S2＝850
N2＝600
トナー（重量％）
スチレンアクリル樹脂 68
マグネタイト 30
負性荷電制御剤 ２
外部交番バイアス電源６
周波数 400Hz
振 幅 1500PP
に於て、スリーブ１上のトナー層厚は約80μで、
階調性良好な画像が得られたが、粒径8μ以下の
もの60％以上を有する微粉トナーを使用した場合
若干の白地カブリが生じた。
本発明は斯る問題点を解決するもので、第３
図・第４図は本発明の基本構成である。
実施例 （第３図）
磁極N1の中心を現像中心位置からθ（約18゜）
磁性ブレード３の方にずらしθ1＝96゜，θ2＝78゜と
したもので、他の各数値条件は第１図に示した例
と同じ。この構成により上述の例に生じた地カブ
リが消えた。その理由は次のように推定される。
磁極N1（850G）のずれにより、現像中心位置
での垂直（ドラム５・スリーブ１の回転軸心を結
ぶ線）方向磁場は350G、これに直角な水平方向
（スリーブ１の面に平行な方向）の磁場成分500G
である。
第４図は磁極N1の近傍でのトナー配列の様子
を模型的に示したもので、磁極中心Ｙ線上の磁場
は垂直成分Ｇ１のみで、鎖状のトナーT1は感光
ドラム１に向つて立つている。磁極よりずれた位
置Ｘでは水平方向の磁界成分G2が強く、鎖状ト
ナーT2は、現像剤担持体（スリーブ１）上に寝
ている。
このためＸ位置の方向がトナー粒子同志の拘束
力が強く、その拘束力に打ち勝つてスリーブ１か
らトナーを吸引するに必要な静電潜像の電位の値
（電界閾値）が大きくなり、交流バイアス効果に
より、潜像の高電位部での画像部の濃度は充分に
得られる一方、潜像の低電位部（白地部）ではト
ナーの転移閾値が大きく、カブリが押さえられる
ものと考えられる。
実施例 （第５図）
潜像領域中心位置は、２つの異なる磁極Sp・
Npの中央に位置する。そして次の関係にあるも
ので、他の数値条件は実施例と同じである。
Sp＝700G θ１＝40゜
Np＝700G θ２＝80゜
S1＝500G θ３＝60゜
N2＝500G θ４＝50゜
S2＝500G θ５＝60゜
N1＝800G
この場合Ｄ位置での水平方向磁界は600G、垂
直方向磁界は０であつた。この条件のもとで、カ
ブリのない極めて鮮明な画像が得られた。
水平磁界密度は300ガウス以上あれば、特にカ
ブリ防止効果が安定することが判明した。
The present invention relates to a developing device using magnetic toner. Conventional developing methods for electrophotography, electrostatic recording, etc. are roughly divided into dry developing methods and wet developing methods. The former method is further divided into a method using a two-component developer and a method using a one-component developer. The one-component developing method has the advantage that it does not have the drawbacks of the two-component developing method, such as fluctuations in the density of the developed image due to changes in the mixing ratio of toner and carrier, and deterioration in image quality due to deterioration of the carrier due to long-term use. It's excellent. Among the one-component development methods, there are powder cloud methods other than the so-called jumping development method, methods called contact development or donor development in which toner particles are brought into direct contact with the electrostatic latent image surface, and methods in which magnetic conductive toner is brought into static contact with the electrostatic latent image surface. In both magnet-dry methods, in which the toner is brought into contact with the electrolatent image surface, the toner comes into contact with the entire surface of the surface to be developed, that is, both the image and non-image areas, so the toner adheres to the non-image areas, resulting in so-called ground capri and dirt. There are some problems that can easily occur. In the jumping development method, toner is uniformly applied to a support such as a sheet, and then the toner is placed facing an electrostatic image holding surface at a small distance, and the toner is attracted from the support by the electric charge of the electrostatic latent image. This is a method in which the latent image is attached to the surface holding the latent image and developed.
9475, U.S. Patent No. 2839400, etc.). This method has the advantage that not only the toner is not attracted in the non-image area where there is no electrostatic charge, but also the toner and the non-image area do not come into contact with each other, so that capri is less likely to occur in the other one-component developing methods mentioned above. However, it is difficult to apply the toner uniformly to the developer supporting means in a practical manner. There is a problem in its practical application because it is difficult to apply and maintain the developer on the developer support means without causing the developer to aggregate during repeated use. Therefore, as disclosed in Japanese Patent Application Laid-Open No. 54-43037, the present applicant has applied a toner onto a developer support while controlling its thickness using a thickness regulating means (hereinafter referred to as a magnetic blade) made of a magnetic material or a magnet. developed a method to do so. In addition, since the jumping development method tends to have high γ characteristics and poor gradation reproducibility, in this regard, the gap between the developer supporting means and the electrostatic latent image holding means is This was improved by applying a low frequency AC voltage as a developing bias electric field. The present invention involves a developer carrier that rotates while supporting a developer layer having a magnetic material, and is transported to a development site that forms the closest gap to the latent image carrier, and an alternating electric field is applied to the development site. and a stationary magnet disposed inside the developer carrier such that the development region is located between two magnetic poles of different polarity. . That is, in the present invention, alternating electric fields are applied to the development site. This alternating electric field causes the developer to be transferred from the developer carrier to the latent image carrier, and then the developer is separated from the latent image carrier, repeating the process.
Finally, an amount of developer is deposited in accordance with the potential of the latent image, and development is performed. According to the present invention, the development region to which the alternating electric field is applied is located between two magnetic poles of different polarities of a fixed magnet included in the developer carrier. Therefore, a magnetic closed circuit formed between the two magnetic poles acts on the development site. This magnetic closed circuit causes the developer connected in a chain along the lines of magnetic force to lie on the side of the developer carrier, thereby increasing the force of restraining the developer on the side of the developer carrier. As a result, a threshold value beyond which the developer is transferred from the developer carrier to the non-image area of the latent image carrier during the phase of the transfer direction of the alternating electric field is increased, and the developer transfer to the non-image area is increased. suppress,
As a result, although the developing device is of a type in which the developer is repeatedly transferred to the latent image carrier by alternating electric fields, it has the effect of improving the antifogging effect. The present invention is applicable to the Carlson process, the applicant's NP process, and other magnetic recording devices, regardless of the structure of the latent image holding member, the latent image forming process, etc. The drawings will be explained in detail below. In FIG. 1, 1 is a sleeve as a developer carrier that rotates around a stationary magnet 2 contained therein, and 3 is a toner layer thickness regulating member (blade) made of a magnetic material (for example, made of iron) that faces the sleeve 1. The thickness of the toner 4 applied onto the sleeve 1 is controlled by the magnetic field formed by the opposing magnetic pole N1. The latent image holder 5 is, for example, a photosensitive drum having a positive potential pattern, and rotates in the same direction as the sleeve 2 at substantially the same speed. The sleeve 1 and the drum 5 form a development area D near their closest parts. Gap A between both 1 and 5 in the area D
is formed larger than the gap B between the sleeve 1 and the blade 3. Reference numeral 6 denotes an AC voltage bias power supply applied between the sleeve 1 and the drum 5, and an example is shown in which it is connected to the grounded back electrode of the photosensitive drum 5 and the shaft of the sleeve 1. The alternating current voltage is, for example, a distorted sine wave alternating current shown in FIG. This alternating electric field causes the toner to reciprocate in the development area D to promote development. FIG. 1 shows a conventionally proposed example in which the magnetic pole S 1 is located near the closest portion of the photosensitive drum 5 and the sleeve 1. This example has the following specifications: Gap (μ) A=300 B=250 Magnetic force density on magnetic pole sleeve (Gauss G) S 1 = 650 N 1 = 850 S 2 = 850 N 2 = 600 Toner (wt%) Styrene acrylic resin 68 Magnetite 30 Negative Charge control agent 2 External alternating bias power supply 6 At a frequency of 400Hz and an amplitude of 1500PP, the toner layer thickness on the sleeve 1 is approximately 80μ,
Although an image with good gradation was obtained, some white background fogging occurred when a fine powder toner having 60% or more of particles with a particle size of 8 μm or less was used. The present invention solves such problems, and the third aspect is
Figure 4 shows the basic configuration of the present invention. Example (Figure 3) Center of magnetic pole N1 is θ (approximately 18 degrees) from the development center position.
The magnetic blade 3 was shifted by θ 1 =96° and θ 2 =78°, and the other numerical conditions were the same as in the example shown in FIG. With this configuration, the background fog that occurred in the above example disappeared. The reason is presumed to be as follows. Due to the misalignment of the magnetic pole N 1 (850G), the magnetic field in the vertical (line connecting the rotation axes of drum 5 and sleeve 1) direction at the development center position is 350G, and the magnetic field in the horizontal direction (parallel to the surface of sleeve 1) perpendicular to this is 350G. ) magnetic field component 500G
It is. FIG. 4 schematically shows the toner arrangement near the magnetic pole N 1 . The magnetic field on the magnetic pole center Y line has only a vertical component G 1 , and the chain-shaped toner T 1 is directed toward the photosensitive drum 1. standing. At a position X shifted from the magnetic pole, the horizontal magnetic field component G 2 is strong, and the chain toner T 2 lies on the developer carrier (sleeve 1). Therefore, the binding force between the toner particles is strong in the direction of the X position, and the potential value (electric field threshold) of the electrostatic latent image necessary to overcome the binding force and attract the toner from the sleeve 1 becomes large, and the AC bias As a result of this effect, sufficient density can be obtained in the image areas in the high potential areas of the latent image, while the toner transfer threshold is large in the low potential areas (white background areas) of the latent image, and it is thought that fogging can be suppressed. Example (Fig. 5) The center position of the latent image area is located between two different magnetic poles S p and
Located in the center of N p . The following relationship exists, and other numerical conditions are the same as in the example. S p = 700G θ1 = 40°N p = 700G θ2 = 80°S 1 = 500G θ3 = 60°N 2 = 500G θ4 = 50°S 2 = 500G θ5 = 60°N 1 = 800G The horizontal magnetic field was 600G, and the vertical magnetic field was 0. Under these conditions, extremely clear images without fog were obtained. It has been found that the fog prevention effect is particularly stable when the horizontal magnetic field density is 300 Gauss or more.
【図面の簡単な説明】[Brief explanation of drawings]
第１図は本発明の前提となる現像装置の縦断側
面図、第２図は交番バイアス電界の説明図、第３
図は本発明現像装置の縦断側面図、第４図は本発
明の作用説明模型図、第５図は本発明の他の実施
例の側面図。
１は非磁性スリーブ、２は磁石、３は磁性ブレ
ード、４はトナー、５は感光ドラム、６は交番電
界電源。
FIG. 1 is a longitudinal cross-sectional side view of the developing device that is the premise of the present invention, FIG. 2 is an explanatory diagram of an alternating bias electric field, and FIG.
4 is a schematic diagram illustrating the operation of the present invention, and FIG. 5 is a side view of another embodiment of the present invention. 1 is a non-magnetic sleeve, 2 is a magnet, 3 is a magnetic blade, 4 is a toner, 5 is a photosensitive drum, and 6 is an alternating electric field power supply.